In recent years, demands for a glass substrate as the base material (substrate) of information recording mediums as represented by a magnetic hard disk drive are increasing.
In order to realize a higher recording density of an information recording medium, the glass substrate as the substrate is subject to a plurality of polishing steps with a high degree of accuracy such as a rough polishing step, a precision polishing step, and so on. In the foregoing polishing steps, high smoothness and high cleanliness of the glass material is demanded, and the improvement of productivity is also required.
As a method of achieving high smoothness, known is the method of using silica-based abrasive grains such as colloidal silica in the final polishing step, and the cyclic use of the silica-based abrasive grains is known as the means for simultaneously improving the productivity (Patent Document 1).
Meanwhile, environmental measures are being sought by society. Information recording mediums such as hard disk drives (HDD) are no exception, and various demands such as low noise and low energy are being made. For instance, a glass raw board that is used as the substrate of the foregoing information recording mediums is demanded of the non-inclusion of antimony, which is used for defoaming. As an alternative component of antimony, cerium oxide is often used. Roughly 0.1 to 2 mass % of cerium oxide is contained in the glass raw board composition.    Patent Document 1: Japanese Patent Application Publication No. 2008-246645